Nowadays, a wide variety of manufacturing machines having specifically-defined fabrication chambers are used for fabricating products and/or components. Often, one or more components can be produced in a single production run in the fabrication chambers of these manufacturing machines, due to the type of production method. Such methods and devices are generally known, for example, by the term “Solid Freeform Fabrication” (SFF-systems) and basically include, for example, production methods and production machines, which are able to produce three-dimensional components directly from 3D-CAD-data. This term further includes all known rapid prototyping and rapid manufacturing methods.
A common feature of all known SFF-systems is the layer-by-layer construction of a workpiece. In recent years, SFF-systems have been used, in which the individual layers are made of a powder or powder-like materials. In particular, metallic components are produced in a melting phase by laser sintering or electron beam melting. “Selective laser sintering” (SLS method) also works according to this principle. In “selective mask sintering” (SMS method), instead of a laser beam, a wide-surface radiation source, e.g., an array of infrared radiators, is used for curing and/or solidifying defined layer areas. A mask determines which areas of a layer will be cured and/or solidified and the mask has to be newly generated for each layer.
All these methods are based on initially applying a layer of loose, i.e. non-solidified, coating material, which has an accurately defined layer thickness and shaped surface (usually a planar surface). The layer-buildup methods used together with the present teachings may be, for example, the following methods: 3DP of the company Zcorp, Polyjet of the company Objet, SMS of the company Sintermask, SLS and DMLS of the company EOS, SLA as well as IMLS of the company 3D Systems, LaserCUSING of the company Concept Laser, laser melting of the company MCP, Electron Beam Melting of the company Arcam, and Electron Beam Sintering.
The above-mentioned layered construction (rapid prototyping) systems have been known for a long time for rapid and cost-effective production of prototypes or small series production. The primary application of previously-used rapid prototyping systems has been the production of components made from organic materials like polymers and waxes. Rapid prototyping systems are, however, also increasingly being used in the production of metal components. In particular, metal components are produced in a melting phase by laser sintering or electron beam melting.
In the above-mentioned methods, 3D CAD data is typically first broken up into a plurality of individual layers or vertical sections and then the workpiece built up or fabricated in the actual production process based upon these individual layers or sections. That is, body outline data must exist for each layer in all known layered construction methods for producing three-dimensional bodies. Body outline data precisely specifies in each layer, which areas of the layer have to be melted or sintered in accordance with the type of layered construction technology used. Such a method is described, for example, in WO 2005/090448 A1. In this case, a layer is produced by applying a powder layer of a predetermined thickness on a base or an already-produced layer and then selectively solidifying this powder, for example, by laser irradiation in the areas that form each layer of the shaped body, thereby bonding it with the solidified areas of the previous layer which are positioned beneath. After completion of the top layer, the non-solidified powder is removed, so that only the shaped body made of the solidified powder is left. A prerequisite for these methods is a powder as a starting material that, on the one hand, can be applied on a base in layers having a defined thickness and, on the other hand, can be selectively solidified in a well-defined manner by targeted fusing, or sintering, or by contact with a liquid that cross-links the powder, thereby undergoing a mechanical bond with the already solidified areas of a previous layer.
The production of such powders, which are, e.g., made of metals, metal alloys or thermoplastics, in particular polyamides having a long hydrocarbon chain between the amide groups, like PA 11 or PA 12, is relatively costly, because the powder particles must have dimensions (diameter, largest diameter to smallest diameter in elliptical particles, surface roughness, etc.) that are defined within narrow limits.
It is also known from WO 2005/090448 A1 to admix additives, such as glass spherules, aluminum flakes or also stiffening or reinforcing fibers, e.g., carbon, glass, ceramic, or boron fibers, into the thermoplastic powder in order to improve its mechanical characteristics, wherein the volume fraction of said additives may amount to up to 30% of the powder and wherein their length distribution is chosen such that the percentage of fibers protruding from the surface of the powder particles, into which the fibers are incorporated during production, is as small as possible. This ensures that the cross linking of powder particles and/or the solidification of the powder is not impaired during the laser irradiation.
In EP 1 058 675 B1 and U.S. Pat. No. 4,938,816, methods for laser sintering are disclosed wherein a ceramic powder or other powder is used. A device for laser sintering, in particular, metal powder is known from DE 195 14 740 C1. A device and a method for building up fluids are disclosed in DE 10 2004 008 168 A1. Finally, it is known from this prior art to compact the powder during laser sintering or to compact a layer during or prior to the solidification using the laser means in order to achieve a high volume density.
The known devices and methods may, however, have the disadvantage that the coating material forming the individual layers is expensive and, under certain circumstances, may either only function in a very narrow process window or may have a low margin of error. Further, such methods may also make particularly high demands on the materials to be used, as the forces involved in the coating process are dependent on the flowability of the powders and the viscosity of the pastes, respectively. In particular, in contrast to spherical powders, so-called irregular or fiber-shaped powders may be problematic to process using conventional devices and methods, or may not attain sufficient powder density during the coating, in order to achieve a sufficient component density during processing. Therefore, powders having spherical particle geometries are often used, which powders are frequently mixed with flow improvers, such as, for example, carbon black or SiO2 in order to make these powders usable for conventional coating devices.
The known layering methods and devices may cause difficulties when the surface to be coated exhibits different states, e.g., when unhardened material and hardened material are present or when loose powder and fused powder are present.